It was a great video indeed. The only thing that I wonder is if there is a difference between "shading" a cell or covering it up completely like they did with the cardboard. I know that seems overly critical but rarely does a cell have something literally over it. When there is shade, there is still scattered light, so maybe it wouldn't have dropped so much?

I don't know that answer, but when we do solar we will do parallel due to this video.

Just be aware these are 12v panels only. The better choice would be the higher 37v panels like used in the normal house solar install. Will have to try that test on my boat sometime. It has a nominal 80 v into a outback. I believe the "bypass diodes" are more applicable to the higher voltage panels but may be wrong. Also more cost effective to be using the panels used in house solar?

Just be aware these are 12v panels only. The better choice would be the higher 37v panels like used in the normal house solar install.

37v panels are identical to two "12v" panels connected in series. The only difference is the higher voltage panel is housed in one frame.

If two "12v" panels are connected in series and placed together they will be identical to single larger 37v panel of the same wattage (assuming the other characteristics of the cells such as temperature coefficients etc are the same)

If parallel connection is best for "12v" panels it is even more important that higher voltage panels are connected in parallel.

All solar panels that a boat is likely to use will have (or should have, some of the very cheap no name panels have been known to leave them out)) bypass diodes. Their primary purpose is to protect the cells from overheating if there is partial shade, but they do increase the output especially in series. If you use series connection adding an extra bypass diode around the whole panel is sensible.

My internet connection is too slow to see the video, but they should indicate the properties of the panels they are testing. If there are no bypass diodes that will effect the results.

I still have an open mind, but I think most of the evidence points to parallel connection as superior to series connection on a boat providing the wiring is adequate. If this is true if also indicates, if all other things are equal, "12v" panels are superior to higher voltage panels. Of course things are not equal, high efficiency large 12v panels are not produced.

It is also possible that a combination of series and parallel connection of solar panels is best. It is worth rembering the individual cells in solar panels are connected in series so technically even if we wire the panels up in a parallel we actually have the solar cells arranged in a series/parallel configuration.

The question we should be really asking is what is the optimum number of solar cells that we should be connecting in series. It is unlikely that the correct answer is always 36 (as occurs in a "12v"panel). If we knew this ideal number of cells we could wire up both 12V and high voltage panels to be as close as possible to this optimum.

I started this thread almost 5 years ago and it surprising given the widespread use of solar on yachts that we still do not have a definitive answer.

I haven't been able to view the video (low bandwidth), but I infer it shows dramatic power output declines with minimal shading. I've not done analytic testing on our system, but I do monitor via Victron meter. Shading absolutely kills the power output of our panels, and it doesn't seem to take a lot. Even diffuse shading from the mast/shrouds/halyards is enough to cut power output significantly. For example, I watched as we went from ~14 amp input to ~-5 amp while drawing about 7 (fridge running) just due to diffuse mast shading. Later afternoon sun, us swinging facing west, mast shading as we swung.

This is why I wired our four panels in parallel. I figured (rightly it seems) that this would usually allow at least 1/2 the panels to be working most of the time.

The video clearly shows that parallel is better than series when panels are being used where there might be shading, even partial shading. Through my own experience of having 30 cell 33 cell and 36 cell panels I know 36 is the minimum requirement to get the voltage needed to charge batteries fully. For maximum output for a given space( where there's shading) smaller panels are better, but larger panels are a better buy. And as already stated when you get really large panels most are two smaller panels in one frame.( if they're rated for 12 volts).